COMPARATIVE ANALYSES OF PETROGRAPHIC AND PHYSICOMECHANICAL PROPERTIES OF SELECTED GNEISSES FROM OKENE, SW BASEMENT COMPLEX, NIGERIA

Abstract

In an attempt to determine the more suitable gneiss for foundation works (house, road, and dam construction), the need arises to search for geomaterials that will help to minimize the cost of executing durable engineering projects. Selected samples of gneisses’ petrographic and physico-mechanical properties were examined to ascertain which type of gneiss is more suitable for engineering projects. Physico-mechanical and petrographic analyses were done on 10 representative samples, 5 each for granite gneiss and granodiorite gneiss taken randomly from different outcrops in Okene. The cores were prepared to meet the recommended heights/diameter (H/D) ratio of 2 – 2.5. The results show the mean values of minerals such as quartz (28%), orthoclase (26%), plagioclase (22%), biotite (10%) and muscovite (12%) for granite gneiss and quartz (30%), orthoclase (16%), plagioclase (31%), biotite (9%) and muscovite (7%) for granodiorite gneiss respectively. The granite gneissis is medium-coarse grained with persistent
foliation and minor evidence of mineral alteration, while the granodiorite gneiss is fine-medium grained characterized by discontinuous foliation. The Uniaxial compressive strength (UCS) of granite gneiss was between 57.8 Mpa and 142.2 Mpa and is strong to very strong rock and is designated as very strong to strong rock while granodiorite gneiss with UCS between 57.6 Mpa and 88.1 Mpa and is designated as strong rock .In comparison. The mean values of water absorption capacity (WAC) of granite gneiss (0.66%) and (0.65%) for granodiorite gneiss fell within permissible limit of <1.00 %.